Improvement in lifting-jacks



UNITED STATES PATENT OFFICE,

ALEXANDER DUNCAN, OF DUNCANS MILLS, CALIFORNIA.

IMPROVEMENT IN LIFTING-JACKS.'

Specification forming part of Letters Patent N0. 171,107, dated December 14, 1875; applicationled May 17, 1875.

To all whom it may concern:

Be it known that I, ALEXANDER DUNCAN, of Duncans Mills, Sonoma county, State ot' California, have invented a "new and useful Improvement in `Lumber-Jacks, of which the following is a specification:

My invention relates to that class of liftingjaoks used in the lumber trade to raise and handle heavy logs; and it consists in making the frame casting in a better shape, or, more particularly, in making the face-plates in which the gearing is held that works the rack on the lifting-bar of such `form that they shall resist the great strain put upon them and hold the parts together without springing or twisting, as will be more fully described hereinafter.

Figure 1 of the accompanying drawing is a side elevation of a lumber-jack, showing the plates A A', between which the gearing works, the lifting-bar B, with a rack on its side, and the crank C, by means of which the bar B is operated, through the medium ot' a pinion 011 the shaft ot' the crank and a spur- Wheel en,`gagin,( j` with it and with the rack of the lifting-bar. These several parts are combined, as shown, with a bar or block of wood of suitable size, and logs are raised by it through the action of the gears worked by the crank to raise the lifting-bar.

In Fig. 2 is shown my improved. manner of making the face-plates which form the top part ot' the jack, Where the strain is the great-4 est, and furnish supports and bearings for the rack and gear.

This casting is made in two parts, a a', one of these having a projecting lug, b, at top and bottom, ot the shape shown, with bolt-holes o c running` entirely through the lugs at each side, and the other, a', with its inner face a plane, excepting at the points that come against the tace otl the lugs b b when the plates are joined together by the bolts and nuts d, and at this .i point the inner face of the plate a has a small rib, both at its upper and lower ends, corresponding to the line of the lugs b on the opposite plate, so that when the two plates are brought together and secured by the bolts and nuts there will be formed a slot, D, ot'quadrilateral form, at the top and bottom of the plates. These slots will be of proper size to permit the lifting-bar B to work smoothly up and down within them.

This provides a strong and rigid bearing of metal all around the bar where it Works between the plates al a', and prevents springing of the plates by any twist or unequal strain brought upon the bar B.

The form of lumber-jack now in general use has its upper end strengthened by the two Hat plates placed one on each side ofthe block or wood-work of the jack, with a strap or band around theln, in addition to the bolts and nuts, to keep them from separating under the strain, and the lifting-bar works up and down in a slot in the wood and against the inner face of the plate A' but this arrangement is Weak, and the plates are liable -to be thrown out ot' line, and the gearing held between them injured or broken by reason ot' their bearings being thrown out of place; and, further, as the liftingbar has no rigid supportfor its sides to Work against, it is frequently thrown out ot line when the pressure or weight upon its lower end is unequal, or not in a line with the motion of the bar in a perpendicular direction, and in suoli case, the pressure of the bar being brought more against one side of the Wood-work around it than against the other, the slot in which it works will soon become enlarged, and a lateral motion ot the bar be permitted by the improper size of the slot 5 but, by the construction and arrangement of my plates, the lifting-bar not being in contact with the wood, or not depending upon it in any manner for' support at the points where it extends beyond the plates, there is no liability oi' the rack or the gearing being inj ured or thrown outI ofplace with each other.

These plates are made of chilled east metal, and are held together by the bolts and nuts at top and bottom, which pass through the lugs, as before described. They embrace the wood-Work forming the frame ot' the jack, and prevent any springing of the parts constitutting the lifting mechanism.

Having thus fully described my invention, what I claim therein as new is- The face-plates, when made in the form shown andvdeseribed, and united together by scribed my name this 19th day of April, A. D. vmenus of the bolts and nuts, so that there 1875. will be a slot of quadrilaterall shape at the top und bottom of the plates to form a bean VALEX' DUNCAN ing and. support for the lifting-bar, as set Witnesses: forth. A t EDWD. E. OsBoRN,

In Witness whereof I have hereunto sub- M. E. CARPENTER. 

